Previous attempts to produce unsaturated aldehydes by vapor phase oxidation of propylene, similar to the present invention, are disclosed in U.S. Pat. No. 3,454,630 and Canadian Pat. No. 781,513.
In U.S. Pat. No. 3,454,630, propylene is oxidized to produce acrolein by the use of a catalyst represented by the formula Ni,Co,Fe,Bi,P,Mo,O and the maximum single pass yield* of acrolein is 71 percent. In Canadian Pat. 781,513, the maximum single pass yield of acrolein amounts to 75.5 percent by the use mainly of a catalyst represented by the formula Ni, Co, Fe, Bi, As, Mo, O. A major objective of this invention is to provide a catalyst which, when used in a process of oxidizing propylene to acrolein, is capable of attaining an increased acrolein yield. ##EQU1##